Valve assembly having a pressure responsive detent mechanism

ABSTRACT

A fluid control spool valve for directing operating fluid from a high pressure source for moving a fluid-operated motor in forward or in reverse is disclosed. The valve automatically moves to neutral position upon loss of fluid pressure by the operation of a centering spring that is adjusted to move the spool to neutral position when a pressure responsive detent becomes nonfunctional. A second spring maintains the detent operative when the operating fluid is at high pressure but makes the detent inoperative when the operating fluid is at low pressure whereupon the spool is automatically moved to a neutral position.

United States Patent Schexnayder Feb. 18, 1975 [54] VALVE ASSEMBLY HAVING A PRESSURE 3,511,276 5/1970 lessen et a1 137/624.27 RESPONSIVE DETENT MECHANISM 3,680,583 8/1972 Clair 137/62427 X {75] Inventor: Lawrence F. Schexnayder, Joliet, 111. Primary Exuml-ner charles J Myhre [73] Assignee: Caterpillar Tractor Co., Peoria, Assislam Emmi/F4121 [41241118 Calif. Attorney, Agent, or FirmPhill1ps, Moore, Weissenberger Lempio & Strabala [22] Filed: Oct. 9, 1973 [2]] Appl. No.: 404,213 ABSTRACT A fluid control spool valve for directing operating fluid from a high pressure source for moving a fluid- [52] U.S. Cl. 251/297, 137/624.27

operated motor in forward or in reverse [8 disclosed. The valve automatically moves to neutral position upon loss of fluid pressure by the operation of a centering spring that is adjusted to move the spool toneu- [56] References Cited tral position when a pressure responsive detent be- UNITED STATES PATENTS comes nonfunctional. A second spring maintains the 2,757,641 8/1956 Meddock 137/62427 detent operative when the operating fluid is at high TGl'll'llS pressure but makes the detent inoperative when the :{Ockwell operating fluid is at low pressure whereupon the spool acey i l 3,132,668 /1964 Stacey 137/624.27 automancany moved to a neutral poslt'on 3,247,768 4/1966 Tennis 137/6242? X 7 Claims, 1 Drawing Figure REVERSE i1 NEUTRAL- 12829301 21 53 62 t, 58 52 5 FORWARD} jg 1| E 9; 31515 1 a? 25 A l VALVE ASSEMBLY HAVING A PRESSURE RESPONSIVE DETENT MECHANISM BACKGROUND OF THE INVENTION Fluid driven motors are controlled by fluid control systems that employ an operating fluid to effect movement of the motors. Motors driving blades of elevation scrapers, for example, must be moved up and down as well as being retained in a fixed position during operation. Accordingly, the operating fluid must be selectively routed to forward, to reverse and to neutral or non operating position for the motor. For this purpose a directional control spool valve is usually used.

The spool valves usually include a housing having a bore with internal grooves that may be either interconnected to a source of high pressure fluid or blocked from that source by axial movement of the spool which is also provided with grooves that are positioned to engage or to bridge lands separating the grooves within the housing.

In operating devices such as elevating scrapers, it is beneficial if the spool is moved to its desired position by movement of a shifting lever after which a detent mechanism will hold the spool in the desired position so that the operators hands will be free for duties such as steering. Many such detent mechanisms which hold the spool against self-movement but are easily overcome by the force exerted by the operators movement of a control lever are known.

The engine that drives the vehicle is usually employed as the source of power to maintain pressure in the operating fluid. If an engine stops so that fluid pressure is lost, it is more difficult to start the engine when the fluid motor is in forward or reverse because of the extra load on the engine. A more serious problem is that when the fluid motor is in operative position during start-up of an engine, the engine speed at start-up is reduced at a range where damage is done to the engine or at speeds where the resonant frequency of the drive line components is produced which often results in failure of one or more of these components.

The prior art is exemplified by the following US. Pat.

and the following British Specification No.: 1,31 1,897.

SUMMARY OF THE INVENTION This invention comprises a directional control spool valve which overcomes the above-noted problems by providing a detent that maintains the spool of a spool valve in any selected operating position while there is adequate pressure in the operating fluid but which automatically places the spool in neutral position when the pressure of the operating fluid is inadequate, such as when the driving engine stops. The valve of this invention includes the usual valve housing having a fluid inlet and at least three fluid outlets and the internal grooves and lands that are positioned to coact with the grooves in the valve spool upon axial movement of the spool so that the high-pressure fluid from the inlet can be directed to drive the fluid-operated motor in a forward or reverse direction, or it may be directed away from the motor to effect a neutral condition.

Within the valve housing and surrounding the spool, a spool centering device that comprises a slidable spring-containing housing positioned to slide between two extreme positions of engagement with the valve housing. The spring-containing housing includes a compression spring and is engaged by the spool to move it toward one position of engagement with the valve housing when the spool is moved in one direction.

A detent mechanism is provided to hold the spool against movement by the above-described spring in a forward, a reverse or a neutral position. The detent mechanism includes means urged into receiving grooves by a spring which operates between a high spring force position and a low spring force position, and at the high spring force position the detent is urged so strongly into the detent device receiving grooves that it is locked against being moved by the centering spring. However, when there is low spring force as a result of loss of fluid pressure, the detent is not able to retain the spool against movement ofthe force ofthe centering spring. The centering spring is positioned and operative to normally bias the spool to neutral.

BRIEF DESCRIPTION OF THE DRAWING The accommpanying Drawing illustrates a sectional view ofa valve embodying the present invention shown in a schematic of a fluid circuit.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the Drawing, a valve generally indicated by the numeral includes a detent mechanism generally indicated by the numeral ll. The valve includes a valve body or housing 12 which is provided with stepped bores 14, 15 and 16. The housing 12 is provided with inlet ports 18 and 19 for communicating high-pressure operating fluid to the bore outlet ports 20 and 21 for distributing high-pressure operating fluid to a fluid-operated motor 45 and outlet ports 22, 23 and 24 for returning high-pressure operating fluid to a storage tank or sump 42. A valve spool 25 is reciprocably mounted within bore 14 and is provided with lands 27, 28, 29, and 31 formed in the spool which define annular grooves 32, 33, 34 and 35 between them for controlling the communication of fluid between the inlet and outlet ports. The spool protrudes beyond the housing 12 and is provided with a stem 36 for attaching the spool to a manually actuating lever which is not shown that is suitable for use by an operator for moving the valve spool to its forward, reverse or neutral positions, indicated on the drawing.

High-pressure fluid is supplied to inlet ports 18 and 19 by a pump 40 which communicates to the inlet ports through a pair of branched conduits 37 and 38. When the spool 25 is in neutral position, the high-pressure fluid passes through bore 14 via the annular recesses 33 and 34 and is returned to the fluid storage tank 42 through outlet port 23. A return conduit 41 connects port 23 with the fluid storage tank 42. When the valve spool is moved to the forward position, the annular groove 35 permits fluid at high pressure to pass from inlet port 19 to the outlet port 21 which is connected by a conduit 43 to the fluid-operated motor 45. The motor is adapted to move in the forward direction when operating fluid at high pressure passes through conduit 43.

Typically, a hydraulic motor will elevate a blade of an elevating blade scraper when the spool 25 is in the forward position. Fluid exhausted from the motor passes through the motor, through a conduit 46 and enters port 20 which is in communication through annular groove 32 with the port 22 which is connected through a branch conduit 47 to conduit 41 and ultimately to the storage tank 42. When the spool is in the forward position, fluid pressure cannot enter the housing through inlet port 18 because it is blocked by the lands 28 and 29.

When the valve spool 29 is moved to the reverse position, fluid pressure at the inlet port 18 is communicated with the outlet port 20 through the annular groove 32 which in turn provides high-pressure fluid to the motor 45 through the conduit 46. The motor will then move in the reverse direction, for example, lowering the blade of an elevating blade scraper. Fluid exhausted by the motor is carried through conduit 43 to the port 21, through the spool valve 10, through passage 24 and returns to tank 42 through a conduit 48 which connects with conduit 41. In the reverse position the fluid pressure at inlet port 19 is blocked by lands 29 and 30.

The centering device of this invention is generally indicated at 50. The centering device is disposed in the bore 15, and it surrounds a portion of the spool 25 that is of reduced diameter as compared with the portion in bore 14. The centering device includes a slidable, spring-containing housing 52 that moves within bore 15. A snap ring 53 is provided to limit the distance that the housing 52 may slide by causing it to engage the valve housing 12. An inwardly extending flange 54 formed on one end of the sleeve is positioned so that its outer side engages a second snap ring 55 disposed in a groove formed in a reduced diameter portion 51 formed on the spool 25. The inner side of the flange engages one end of a helical spring 56, and the other end of that helical spring abuts an annular retaining ring 57 which abuts both the valve housing 12 at a shoulder 58 and the spool 25 at a shoulder 59. As thus described, movement of the spool 25 to the reverse position causes spring 56 to be compressed because annular retaining ring 57 moves to the right, while moving the spool to the forward position causes the spring 56 to be compressed by moving spring-containing housing 52 to the left. Consequently, the spring 56 urges the spool to its neutral position from either direction of movement.

The detent mechanism generally indicated at 11 includes a number of balls 61 which are retained in the axial position by a carrier or fixed-ring member 62. The carrier 62 is rigidly held between a pairof snap rings 64 and 65 so that it is not axially movable with respect to the bore of the valve housing 12. Three grooves 66, 67 and 68 are'formed on an extension 69 of the valve spool, and these grooves are shaped to receive the balls 61 and are positioned on the extension of the valve spool to hold the valve spool in a suitable position for forward, reverse or neutral as described above. An annular camming ring 70 is slidably mounted about the extension 69 of the valve spool within the bore 15. The ring 70 is provided with a substantially conical face defining an inclined camming surface 71 which is in contact with the balls 61 and adjacent to the carrier 62. A compression spring 72 is positioned in the largest bore 16 and extends into bore so that it exerts force against the ring 70. The opposite end of the spring 72 is held in a retainer 74 which is positioned to slide axially within the bore 16. The retainer 74 has a flange 75 positioned to engage the spring 72 and to maintain a snug fit within the bore 16 and also to serve as stop means. An end cap 77 is mounted to the valve body 12 by bolts 78 to close the outer end of the bore 16. The end cap is provided with a bore 80 in which a piston 81 that works against the spring retainer 74 is maintained. A stem 82 of the piston 81 fits in an aperture 84 in the retainer 74 to aid in the alignment of these movable members. The retainer preferably is fixed on the stem 82 firmly with apress fit.

An inlet passage 87 is provided through the end cap 77, shown herein as through a threaded plug 85. A conduit 88 supplies pressurized fluid from the pump 40 to the inlet passage 87 so that the fluid may act against the piston 81 to compress the spring 72 when the fluid is under high pressure. A conventional pressure relief valve 90 is associated with the conduit 88 to avoid damaging pressure in the fluid system by releasing high 1 transmitted to the piston 81.causing it to move against retainer 74 to compress the spring 72. Spring retainer 74 is limited in its motion from its position as shown in the drawing to a position where it abuts against a shoulder 76 of the valve housing 12. When abutting shoulder 76, the force exerted by spring 72 against annular ring is such that balls 61 are locked into one of grooves, 66, 67 or 68 with sufficient force to prevent the spool 25 from moving because of the action of the spring 56.

.The detent involving balls 61 and one of the grooves 66, 67 or 68 is not held with sufficient force, however, to lock the motion of spool 25'against manual opera tion of a lever to change the spools position among the 1 forward, reverse and neutral positions. Manual operation of a shifting lever places sufficient force on the spool 25 to compress the spring 72 even further so that balls 61 may move apart enough to enter a different groove.

Upon loss of fluid pressure in line 88, the spring 72 expands fully, and in that'position it exerts insufficient force on the annular ring 70 and balls 61 to lock the spool in position against the force of the spring 56. Spring 72 may preferably be completely relaxed when expanded fully. As mentioned hereinabove, the centering spring 56 is compressed when the spool is in either forward or reverse position. Upon loss of fluid pressure in the system, the fluid pressure in line 88 diminishes so that the spring 72 can expand against the piston 81. 1t accordingly pushes retainer 74 back into contact with end cap 77 and theforce exerted by the spring 72 is diminished to the point where the spool 25 is not locked against the action of the compressed spring 56. As a result of the foregoing, upon loss of pressure in the fluid system, spring 56 expands and by this action it automatically places the spool in a neutral position so that high-pressure flud entering the valve via ports 18 or 19 is returned to the reservoir 42 via port 23 without passing through the motor 45.'This action will take place whether the spool was in forward or reverse position upon loss of fluid pressure. If the spool was in neutral position when fluid pressure was lost, it will remain in neutral.

Thus, the valve of the present invention includes a fluid pressure responsive detent mechanism that holds the valve in forward, reverse or neutral position against any movement other than that deliberately effected by an operator when there is operational fluid pressure in the system. If the system loses fluid pressure, the spool valve automatically moves to neutral position thereby avoiding restarting problems and the problems associated with resonant frequencies in linkages. Upon restarting the engine, the detent mechanism is reactuated and holds the valve firmly in neutral position until it is moved to forward or reverse position by the deliberate act of an operator.

It will also be readily appreciated that the pressure responsive detent mechanism is a desirable safety feature in that it prevents the valve from being in an actuated position when the engine is started. Being in an actuated position presents a possible hazard to men working on or around the vehicle because the motor controlled by the valve may start unexpectantly as the engine is started.

What is claimed is:

l. A hydraulic valve assembly comprising:

a valve body having a cylindrical bore and fluid inlet and outlet openings communicating with said bore;

a spool reciprocably disposed in said bore and movable to at least a first operating position to effect communication between said inlet and outlet openings, and to a neutral position to block said communication;

centering spring means for biasing said spool to said neutral position; and

pressure responsive detent means disposed in said valve body and responsive to a predetermined operating fluid pressure to hold said spool in said operating position against the force of said centering spring, and operative in response to a drop in said fluid pressure below said predetermined pressure to release said spool for movement by said centering spring to neutral position,

said detent means comprising a plurality of annular grooves extending around the outer diameter of said spool, a plurality of balls mounted in said valve body surrounding said spool for engagement with said grooves, reciprocal annular camming means extending around said spool externally thereof for engaging and biasing said balls into said grooves, and piston means mounted in said housing and responsive to fluid pressure for biasing said annular camming means into camming engagement with said balls, including resilient means connecting said piston to said annular camming means.

2. The valve assembly of claim 1 wherein said piston means is mounted externally of said spool and axially thereof.

3. The valve assembly of claim 2 comprising a fixed ring member fixed in said bore concentric with said spool adjacent said annular grooves;

said annular camming means comprises a cam ring member having a substantially conical face on one side thereof; and

said balls are confined between said fixed ring member and said substantially conical face of said cam ring member.

4. The valve assemby of claim 3 wherein said resilient means comprises a compression spring.

5. A hydraulic valve assembly comprising:

a valve body having a cylindrical bore and fluid inlet and outlet openings communicating with said bore;

a spool reciprocably disposed in said bore and movable to at least a first operatingposition to effect communication between said inlet and outlet openings, and to a neutral position to block said communication;

centering spring means for biasing said spool to said neutral position;

pressure responsive detent means disposed in said valve body, responsive to a predetermined operating fluid pressure to hold said spool in said operating position against the force of said centering spring, and operative in response to a drop in said fluid pressure below said predetermined pressure to release said spool for movement by said centering spring to neutral position,

said detent means comprising a plurality of annular grooves extending around said spool, a plurality of balls mounted in said valve body surrounding said spool for engagement with said grooves, and camming means including an annular cam member reciprocably mounted in said bore and having an inclined surface engaging and biasing said balls into said grooves, a fluid pressure responsive piston mounted in said valve body, and spring means connecting said piston to said annular cam member.

6. The valve assembly of claim 5 comprising an annular shoulder disposed in said bore, and said balls confined between said shoulder, said spool and said annular cam member.

7. The valve assembly of claim 5 comprising stop means for limiting the movement of said piston. 

1. A hydraulic valve Assembly comprising: a valve body having a cylindrical bore and fluid inlet and outlet openings communicating with said bore; a spool reciprocably disposed in said bore and movable to at least a first operating position to effect communication between said inlet and outlet openings, and to a neutral position to block said communication; centering spring means for biasing said spool to said neutral position; and pressure responsive detent means disposed in said valve body and responsive to a predetermined operating fluid pressure to hold said spool in said operating position against the force of said centering spring, and operative in response to a drop in said fluid pressure below said predetermined pressure to release said spool for movement by said centering spring to neutral position, said detent means comprising a plurality of annular grooves extending around the outer diameter of said spool, a plurality of balls mounted in said valve body surrounding said spool for engagement with said grooves, reciprocal annular camming means extending around said spool externally thereof for engaging and biasing said balls into said grooves, and piston means mounted in said housing and responsive to fluid pressure for biasing said annular camming means into camming engagement with said balls, including resilient means connecting said piston to said annular camming means.
 2. The valve assembly of claim 1 wherein said piston means is mounted externally of said spool and axially thereof.
 3. The valve assembly of claim 2 comprising a fixed ring member fixed in said bore concentric with said spool adjacent said annular grooves; said annular camming means comprises a cam ring member having a substantially conical face on one side thereof; and said balls are confined between said fixed ring member and said substantially conical face of said cam ring member.
 4. The valve assemby of claim 3 wherein said resilient means comprises a compression spring.
 5. A hydraulic valve assembly comprising: a valve body having a cylindrical bore and fluid inlet and outlet openings communicating with said bore; a spool reciprocably disposed in said bore and movable to at least a first operating position to effect communication between said inlet and outlet openings, and to a neutral position to block said communication; centering spring means for biasing said spool to said neutral position; pressure responsive detent means disposed in said valve body, responsive to a predetermined operating fluid pressure to hold said spool in said operating position against the force of said centering spring, and operative in response to a drop in said fluid pressure below said predetermined pressure to release said spool for movement by said centering spring to neutral position, said detent means comprising a plurality of annular grooves extending around said spool, a plurality of balls mounted in said valve body surrounding said spool for engagement with said grooves, and camming means including an annular cam member reciprocably mounted in said bore and having an inclined surface engaging and biasing said balls into said grooves, a fluid pressure responsive piston mounted in said valve body, and spring means connecting said piston to said annular cam member.
 6. The valve assembly of claim 5 comprising an annular shoulder disposed in said bore, and said balls confined between said shoulder, said spool and said annular cam member.
 7. The valve assembly of claim 5 comprising stop means for limiting the movement of said piston. 